The present invention relates to a self-diagnosis apparatus and control apparatus of an engine (internal combustion engine) for use in vehicles such as a car, particularly to a self-diagnosis apparatus for self-diagnosing an abnormality of an air/fuel ratio detection apparatus, and a control apparatus.
In order to purify HC, CO, NOx in an exhaust gas exhausted from an engine, a three way catalytic converter has heretofore been attached midway in an exhaust passage. As shown in FIG. 20, the three way catalytic converter has characteristics that three components of HC, CO, NOx are purified only in the vicinity of a theoretical air/fuel ratio at a high efficiency.
Therefore, in an engine air/fuel ratio control system, as shown in FIG. 21, presence/absence of oxygen in the exhaust gas is detected by an O2 sensor having output characteristics that a sensor output rapidly changes at the theoretical air/fuel ratio, and the air/fuel ratio is feedback-controlled based on an output of the O2 sensor.
To further highly purify the exhaust gas, as an air/fuel ratio control system in which more precise air/fuel ratio control is possible, as shown in FIG. 22, a linear A/F sensor having linear output characteristics with respect to the air/fuel ratio (oxygen concentration of the exhaust gas) is employed to feedback-control the air/fuel ratio, and this system has spread.
In this air/fuel ratio control system, if the linear A/F sensor causes a trouble for some reason, and the output characteristics of the linear A/F sensor change, the precision of the feedback control to the theoretical air/fuel ratio is deteriorated, and the exhaust gas cannot sufficiently be purified. To solve the problem, a method and apparatus for detecting a change of the characteristics of the linear A/F sensor have heretofore been proposed.
One of conventional techniques of detecting the characteristics change of the linear A/F sensor is disclosed in Japanese Patent Application Laid-Open No. 177575/1996. In the technique, a sensor output change ratio of a point at which a fuel supply amount changes is obtained from a sensor output before and after a fuel amount supplied to the engine is changed during fuel cut starting or resetting, and it is judged based on the sensor output change ratio whether or not there is an abnormality in the linear A/F sensor.
Another technique is disclosed in Japanese Patent Application Laid-Open No. 270482/1996. In the technique, when a target air/fuel ratio shifts with a change of engine operation conditions, according to a result of comparison of a change amount of the target air/fuel ratio with the change amount of the sensor output, or a result of comparison of the change amount of the target air/fuel ratio with the change amount of a fuel injection correction amount, it is judged whether or not there is an abnormality in the sensor.
In actual, the characteristics of the air/fuel ratio control system are influenced by various disturbances, and dispersion exists in an output signal of the linear A/F sensor. Therefore, when frequency of diagnosis (judgment of presence/absence of abnormality) is little, sufficient diagnosis precision cannot be obtained in some cases.
On the other hand, in the aforementioned systems, the diagnosis is performed only in specific operation conditions such as during fuel cut or during change of the target air/fuel ratio, and it cannot be said that there are many diagnosis opportunities. Moreover, it cannot be said that any system is satisfactory in respect of diagnosis precision. Furthermore, when the change amount of the sensor output is calculated, the diagnosis is easily influenced by noise, and the diagnosis precision is supposedly similarly deteriorated.
The present invention has been developed to solve the aforementioned problem, and an object thereof is to provide a self-diagnosis apparatus which can detect a response characteristics change of a linear A/F sensor and an operation state of an engine in a short time in almost all operation conditions with high precision, and a control apparatus for appropriately controlling the operation state of the engine.
To achieve the aforementioned object, according to the present invention, there is provided an engine self-diagnosis apparatus comprising: means for controlling an air/fuel ratio of each cylinder of a multiple cylinder engine; air/fuel ratio detection means for emitting an output which is proportional to an air/fuel ratio of an exhaust tube assembly; means for controlling the air/fuel ratio of each cylinder to be non-uniform; and means for detecting response characteristics of the air/fuel ratio detection means or response characteristics of engine control from an amplitude of a signal obtained from the air/fuel ratio detection means under control under which the air/fuel ratio of each cylinder is non-uniform.
Thereby, a vibration of the air/fuel ratio of the exhaust tube assembly generated when the air/fuel ratio of each cylinder is set to be non-uniform is detected, and the response characteristics of the air/fuel ratio detection means or the response characteristics of the air/fuel ratio control system can be detected from the amplitude.
Moreover, the engine self-diagnosis apparatus of the present invention detects the response characteristics of the air/fuel ratio detection means or the response characteristics of the engine control from the signal amplitude based on an engine rotation number in response to the signal obtained from the air/fuel ratio detection means.
A cycle of the vibration of the air/fuel ratio in the exhaust tube assembly generated when the air/fuel ratio of each cylinder is set to be non-uniform depends on the engine rotation number. Therefore, the response characteristics of the air/fuel ratio detection means or the response characteristics of the engine control are detected from a signal component amplitude synchronized with the engine rotation number in response to the signal obtained from the air/fuel ratio detection means.
Moreover, the engine self-diagnosis apparatus of the present invention includes means for judging that the response characteristics of the air/fuel ratio detection means are abnormal when the amplitude of the signal obtained from the air/fuel ratio detection means indicates a predetermined value or less.
Furthermore, the engine self-diagnosis apparatus of the present invention detects a fuel property from the amplitude of the signal obtained from the air/fuel ratio detection means when the engine cools down.
When the engine cools down, the response characteristics possibly change in accordance with the fuel property. Therefore,when the response characteristics of the air/fuel ratio detection means are normal, it is judged that the response characteristics change during cool-down depends on the fuel property.
Moreover, according to the present invention, there is provided an engine self-diagnosis apparatus comprising: means for controlling an air/fuel ratio of each cylinder of a multiple cylinder engine; air/fuel ratio detection means for emitting an output which is proportional to an air/fuel ratio of an exhaust tube assembly; means for controlling the air/fuel ratio of each cylinder to be non-uniform; and means for detecting response characteristics of the air/fuel ratio detection means or response characteristics of engine control from a frequency component of a signal obtained from the air/fuel ratio detection means under control under which the air/fuel ratio of each cylinder is non-uniform.
Thereby, the frequency component of a vibration of the air/fuel ratio of the exhaust tube assembly generated when the air/fuel ratio of each cylinder is set to be non-uniform is detected, and the response characteristics of the air/fuel ratio detection means or the response characteristics of the air/fuel ratio control system can be detected in accordance with a value of the frequency component.
Moreover, the engine self-diagnosis apparatus of the present invention detects the response characteristics of the air/fuel ratio detection means or the response characteristics of the engine control from the frequency component based on an engine rotation number in response to the signal obtained from the air/fuel ratio detection means.
A cycle of the vibration of the air/fuel ratio in the exhaust tube assembly generated when the air/fuel ratio of each cylinder is set to be non-uniform depends on the engine rotation number. Therefore, the response characteristics of the air/fuel ratio detection means or the response characteristics of the engine control are detected from a signal frequency component synchronized with the engine rotation number in response to the signal obtained from the air/fuel ratio detection means.
Moreover, the engine self-diagnosis apparatus of the present invention detects the response characteristics of the air/fuel ratio detection means or the response characteristics of the engine control from a power of the frequency component in a predetermined phase range based on the engine rotation number in response to the signal obtained from the air/fuel ratio detection means.
Since the air/fuel ratio of the exhaust tube assembly vibrates in synchronization with the engine rotation number, the power of the frequency component in the predetermined phase range based on the engine rotation number is proportional to a change amount of the air/fuel ratio applied only to a specific cylinder. However, when the response characteristics of the air/fuel ratio detection means are deteriorated, the amplitude of the air/fuel ratio of the assembly is reduced. Therefore, a proportionality factor of a proportionality of the air/fuel ratio change amount applied only to the specific cylinder to the power of the frequency component changes. Therefore, response deterioration of the air/fuel ratio detection means can be detected.
Moreover, the engine self-diagnosis apparatus of the present invention includes means for judging that the response characteristics of the air/fuel ratio detection means are abnormal when the power of the frequency component in the predetermined phase range based on the engine rotation number indicates a predetermined value or less in response to the signal obtained from the air/fuel ratio detection means.
Furthermore, the engine self-diagnosis apparatus of the present invention includes means for informing that the response characteristics of the air/fuel ratio detection means are judged to be abnormal.
Additionally, the engine self-diagnosis apparatus of the present invention detects a fuel property from the frequency component of the signal obtained from the air/fuel ratio detection means when the engine cools down.
When the engine cools down, the response characteristics possibly change in accordance with the fuel property. Therefore, when the response characteristics of the air/fuel ratio detection means are normal, it is judged that the response characteristics change during cool-down depends on the fuel property.
When it is judged that the response characteristics of the air/fuel ratio detection means are abnormal, control performed based on the signal obtained from the air/fuel ratio detection means is stopped.
Moreover, an engine control apparatus according to the present invention includes means for controlling an engine operation parameter based on response characteristics of air/fuel ratio detection means or response characteristics of engine control.
Thereby, variable gain control of PI control in a theoretical air/fuel ratio correction term calculator can be performed based on the response characteristics of the air/fuel ratio detection means or the response characteristics of the engine control.